1. Field of the Invention
The present invention relates to a magnetic material used for magnetic refrigeration.
2. Description of the Related Art
Most of refrigeration technologies for use in a room temperature region such as refrigerators, freezers, and air-conditioners use a gas compression cycle. But, the refrigeration technologies based on the gas compression cycle have a problem of causing environmental destruction associated with the exhaustion of specific freon gases to the environment, and there is also concern that substitute freon gases have an adverse effect upon the environment. Under the circumstances described above, clean and highly efficient refrigeration technologies, which are free from environmental problems caused by wastage of operating gases, have been demanded to be put into practical use.
Recently, magnetic refrigeration is being increasingly expected as one of such environment-friendly, highly efficient refrigeration technologies. Research and development of magnetic refrigeration technologies for use in a room temperature region is underway. The magnetic refrigeration technologies use the magnetocaloric effect of magnetic material instead of freon gases or substitute freon gases as a refrigerant to realize a refrigeration cycle. Specifically, the refrigeration cycle is realized by using a magnetic entropy change (ΔS) of the magnetic material associated with a magnetic phase transition (phase transition between a paramagnetic state and a ferromagnetic state). In order to realize the highly efficient magnetic refrigeration, it is preferable to use a magnetic material which exhibits a high magnetocaloric effect around room temperature.
As such a magnetic material, a single rare earth element such as Gd, a rare earth alloy such as Gd—Y alloy or Gd—Dy alloy, Gd5(Ge, Si)4 based material, La(Fe, Si)13 based material, Mn—As—Sb based material and the like are known (JP-A 2002-356748 (KOKAI) and JP-A 2003-096547 (KOKAI)). The magnetic phase transition of the magnetic material is in two types including a first order type and a second order type. The Gd5(Ge, Si)4 based material, the La(Fe, Si)13 based material and the Mn—As—Sb based material exhibit the first order magnetic phase transition. These magnetic materials can be used to easily obtain a large entropy change (ΔS) by the application of a low magnetic field but has a practical problem that its operating temperature range is narrow.
A rare earth metal such as Gd and a rare earth alloy such as Gd—Y alloy or Gd—Dy alloy exhibit the second order magnetic phase transition, so that they have advantages that they can operate in a relatively wide temperature range and also have a relatively large entropy change (ΔS). But, the rare earth element itself is expensive, and when the rare earth element or the rare earth alloy is used as a magnetic material for magnetic refrigeration, it is inevitable that the cost of the magnetic material for magnetic refrigeration becomes high.
Besides, it is also known that a (Ce1−xYx)2Fe17 (x=0 to 1) based magnetic material exhibits the second order magnetic phase transition. The (Ce, Y)2Fe17 based magnetic material can operate in a relatively wide temperature range in the same manner as the rare earth element and the rare earth alloy, and it is a substance based on inexpensive Fe, so that the cost of the magnetic material for magnetic refrigeration can be made lower than the rare earth metal or the rare earth alloy. However, the (Ce, Y)2Fe17 based magnetic material has high magnetic anisotropy, so that it has a disadvantage that a magnetic entropy change amount (ΔS) associated with the magnetic phase transition is small.